lx8_6.java

一个简单的Appelet程序,能够绘制四叶玫瑰线

import java.awt.*;
import java.applet.Applet;
import java.awt.event.*;
import java.awt.Color;
public class LX8_6 extends Applet implements ItemListener{
	Color color=Color.black;
	CheckboxGroup cg1;
	Checkbox cb1,cb2,cb3;
	
	public void init(){
		setBackground(Color.white);
		setLayout(new FlowLayout());
		cg1=new CheckboxGroup();
		cb1=new Checkbox("blue",cg1,true);
		cb2=new Checkbox("red",cg1,false);
		cb3=new Checkbox("green",cg1,false);
		cb1.addItemListener(this);
		cb2.addItemListener(this);
		cb3.addItemListener(this);
		add(cb1);
		add(cb2);
		add(cb3);
	}
	
	public void paint(Graphics g){
		int x0,y0,w1,h1;
		w1=600;
		h1=300;
		x0=w1/2;
		y0=h1/2;
		g.setColor(color);
		g.drawLine(x0,10,x0,h1);
		g.drawLine(0,y0,w1,y0);
		int i,j=40,x,y;
		double pi=3.14,angle,r;
		while(j<200){
			for(i=0;i<1023;i++){
				angle=i*pi/512;
				r=j*Math.sin(2*angle);
				x=(int)Math.round(r*Math.cos(angle)*2);
				y=(int)Math.round(r*Math.sin(angle));
				g.fillOval(x0+x,y0+y,1,1);
				}
				j=j+20;	
		}
		setVisible(true);
	}
	
	public void itemStateChanged(ItemEvent e){
		if(e.getSource()==cb1)color=Color.blue;
		if(cb2.getState())color=Color.red;
		if(cg1.getSelectedCheckbox()==cb3)color=Color.green;
		repaint();
	}
   }